The deadly Ebola virus can spread like a forest fire, US health authorities said Monday, urging travelers to West Africa to take extra precautions amid the largest outbreak in history.

Since March, there have been 1,201 cases of Ebola and 672 deaths in Guinea, Liberia and Sierra Leone, the Centers for Disease Control and Prevention said.

Two Americans — one doctor and one healthcare worker — in Monrovia, Liberia have come down with the virus, characterized by fever, joint pain, diarrhea, vomiting and often fatal bleeding.

“The likelihood of this outbreak spreading beyond West Africa is very low,” admitted Stephan Monroe, deputy director of the CDC’s National Center for Emerging and Zoonotic Infectious Diseases.

But, he added, it is a “rapidly changing situation” and the CDC must be “prepared for the very remote possibility” that a sick traveler could bring the disease into the United States.

The CDC issued a level two notice — one notch below a call to avoid nonessential travel to the region — warning people to avoid contact with blood and bodily fluids of sick people in the affected countries.